The present invention relates to a circular knitting machine of the type with cylinder and dial with thread clamping and cutting device for manufacturing open fabric.
In the field of circular knitting machines of the type with cylinder and dial, both with fixed cylinder and dial and with rotating cylinder and dial, machines are known which can manufacture an open fabric instead of a tubular fabric.
In such machines, a sector of the needle cylinder and of the dial has no needles, and at said sector there are appropriate devices which clamp and cut the threads knit by the needles.
More particularly, considering a machine with rotating needle cylinder and dial, the threads for forming the knitting are supplied to the needles at one or more feed regions arranged around and above the needle cylinder. After the last needle before the beginning of the needleless sector has engaged the thread at a feed of the machine, said thread, which remains tensioned between the feed by which it has been supplied and said last needle, is clamped and cut by the clamping and cutting device so that the portion of thread which remains between the needle and said device is retained during the formation of a few successive rows in order to avoid broken meshes. The portion of thread which starts from the feed being considered is instead supplied to the needles which pass by said feed after the needleless sector so as to start the formation of a new row of knitting.
The thread clamping and cutting devices are generally applied to the upper face of the dial at the needleless sector and proximate to the needle knitting region, so that the threads to be clamped and cut can be easily engaged by said devices.
However, this arrangement, which is at first thought the simplest, has some disadvantages.
The clamping and retention of the threads in this region of the machine can in fact hinder the unloading of the last loop formed by the needles which are proximate to the needleless sector.
Furthermore, since safety devices are mounted proximate to the needle knitting region in order to detect anomalies in the operation of the machine, it is necessary to provide appropriate devices which deactivate the safety devices when they are, during the operation of the machine, at the clamping and cutting devices in order to avoid useless stoppages of the machine.
Furthermore, when one wishes to vary the width of the fabric by increasing or reducing the width of the sector at which no knitting is formed, besides moving the clamping and cutting devices it is also necessary to correspondingly move the devices required to deactivate the above mentioned safety devices.
Naturally the width of the sector at which no knitting is formed can be varied by including in the knitting, or excluding therefrom, a certain number of needles which border with the needleless sector of the needle cylinder and of the dial.